The use of wireless communication systems through which to communicate has achieved wide popularity in recent years. In a wireless communication system, a radio link is utilized upon which to form a communication path between a sending station and a receiving station. In contrast to a conventional, wireline communication system which requires fixed, wired connections to be maintained between the sending and receiving stations, use of a wireless communication system inherently permits increased mobility of communication. Additionally, infrastructure costs associated with a wireless communication system are generally less than the corresponding costs associated with the infrastructure of a conventional, wireline communication system. Installation of a wireless communication system is therefore generally less costly than the costs associated with installation of a wireline communication system.
Multi-user, wireless communication systems permit relatively large numbers of users simultaneously to communicate by way of such systems. A cellular communication system is exemplary of a wireless, multi-user, radio communication system which has been installed over significant geographical areas and which has achieved wide levels of usage.
A cellular communication system makes relatively efficient use of the portion of the electromagnetic spectrum allocated thereto upon which to define communication channels. The infrastructure of a cellular communication system includes a plurality of fixed-site base stations which are installed at spaced-apart locations throughout a geographical area. Because of the positioning of the base stations, only relatively low power signals are needed to be transmitted to effectuate communications with a mobile station. By transmitting relatively low-power signals, the same frequencies can be reused at different locations throughout the geographical area in which the network infrastructure installed. Communications can be effectuated between more than one set of sending and receiving stations concurrently at separate locations throughout the area encompassed by the cellular communication system.
In an ideal communication system, data, communicated by the sending station, is communicated distortion-free upon a communication channel to the receiving station. When the data is received at the receiving station, the data is substantially identical in value to the corresponding data when transmitted by the sending station. However, in a non ideal communication system in which the data is communicated upon a non ideal communication channel, the data, when received at the receiving station, is dissimilar to the corresponding values of the data when sent by the sending station. Distortion of the data caused by transmission of the data upon the non ideal communication channel causes such dissimilarities to result. If the distortion is significant, the informational content of the signal cannot be recovered at the receiving station.
The communication channel might be of characteristics which distort the value of the information bearing bits forming the data which is communicated upon the communication channel to the receiving station. Fading, such as that caused by multi-path transmission or Rayleigh fading, alters the data during its transmission. Such distortion, if not corrected, reduces the communication quality levels in a communication session formed between the sending and the receiving stations.
Various techniques are utilized to overcome distortion introduced upon the data as a result of transmission upon a non ideal communication channel.
Time-encoding of the data, prior to its transmission, for instance, increases the redundancy of the transmitted data. By increasing the time redundancy of the data, the likelihood of the informational content of the data being recoverable, once received at the receiving station, is increased. Increasing the time redundancy of the data is sometimes referred to as creating time diversity.
Adaptive modulation is also sometimes utilized. In an adaptive modulation technique, the manner by which the data is modulated is selected responsive to the channel conditions of the communication channel upon which the data is to be communicated. That is to say, the modulation scheme utilized by which to modulate the data is selected according to the channel conditions. High-order modulations are utilized with little, or no, coding when the channel conditions are good. Conversely, low-order modulation schemes with maximum coding are utilized when the channel conditions are poor. Determination of the channel conditions are made through, for instance, evaluation of measured signal-to-noise ratios (SNRs).
The range of possible values of the SNR is partitioned into a number of fading regions. A specific modulation scheme or a specific coding scheme, or a combination of both, is assigned to each region. Selection of the boundaries between regions is important as the boundaries define which modulation and/or coding schemes are utilized to overcome the non ideal channel conditions. The region boundaries shall herein be referred to as switching thresholds as switching between modulation parameters such as the modulation-type and coding-type switch at such boundaries.
In the aforementioned co-pending patent application of Ser. No. 09/751,640, an artificial intelligence learning scheme is utilized to optimize the switching thresholds so as to maximize the data throughput (TP) of the communication of the data from the sending station to the receiving station. With further communication of the data, the long-term data throughput is continuously monitored and values derived therefrom are used as a referee to train the artificial intelligence learning scheme. A manner is thereby disclosed by which to facilitate maximization of data throughput upon a non ideal communication channel.
The use of additional performance criteria, in addition to data throughput, might additionally be utilized in the selection of switching thresholds.
It is in light of this background information related to communication systems which utilize adaptive modulation schemes that the significant improvements of the present invention have evolved.